As the most common electrical energy storage devices, rechargeable battery can supply high energy density, but its low power density and short cycle-life limits some special applications such as high current charge-discharge. Compared with the rechargeable battery, supercapacitor can provide higher power density and more outstanding cycle stability, but their energy density is much lower. Therefore, hybrid of the rechargeable battery and the supercapacitor with qualities of both has been investigated.
A conventional energy storage device with qualities of both the rechargeable battery and the supercapacitor includes a capacitor and a battery electrically connecting with the capacitors, wherein the capacitor and the battery are separate. The conventional energy storage device further includes a voltage control module because the capacitor and the battery have different operating voltages. Thus, the conventional energy storage device has larger volume and higher cost.
What is needed, therefore, is to provide a hybrid energy storage device that can overcome the above-described shortcomings.